I currently have a single instance cluster with 2 nodes and I have a requirement to add a second instance to it (both instances will be live on the same node, so one node will still be 'passive'). I just have the following questions:

1. Can I specify the same network name for the second instance during setup? So the instances would be as follows...cluster1\inst1, cluster1\inst2.2. Does installing a second instance require any additional IP addresses?3. Can the second instance share the same SAN disks as the first, so all the MDF and LDF files are in the same location?

you only need 1 quorum disk resource, period. There are other quorum models available and depending on the number of nodes and geographical location, you could probably do away with quorum disk altogether

With regards to MSDTC, yes you could possibly get away with one resource for both instances especially as they're all going to be active on the same node

Sorry to revive this thread but I have encountered one final dilemma during the SQL Install...!

When installing the second instance to the existing cluster, in addition to giving the new instance it's own Network name, does it have to have a different instance name too or can I have 2 default instances with different network names?